The present invention relates to self-contained heating and cooling systems and more particularly to self-contained systems employing heat pump airconditioning units for accomplishing heating and cooling as well as an auxiliary heating unit.
So-called window, through the wall, and/or packaged terminal heat pump airconditioning systems are all self-contained systems in that they are constructed in a single package-like housing. These systems are generally assembled in production quantities by the manufacturer and shipped to installation sites. This enables the systems to be completely installed simply by emplacing them at an installation site and making connections to an appropriate electrical power supply. Accordingly the systems include all the necessary system operating controls, a refrigerant compressor, a refrigerant reversing valve and indoor and outdoor heat exchangers by which heat is transferred to and from the refrigerant in the system.
Typically these kinds of systems are not designed for heating by operation of the heat pump when outdoor air temperatures are near or below freezing because effective removal of the frozen moisture which accumulates on the outdoor refrigerant heat exchanger is a problem in many installations. Even in installations where removal of frozen moisture from outdoor heat exchangers is not a problem, heat pumps operate at less than maximum effectiveness when outdoor tempertures are below freezing. For these reasons many self-contained systems are provided with an auxiliary heating unit operated exclusively to heat the indoor air when outdoor air temperatures are close to and below freezing.
In order to appropriately schedule operation of the heat pump and auxiliary heating units the systems have been provided with a changeover thermostat which senses outdoor air temperature to prevent operation of the heat pump compressor and enable operation of the auxiliary heating until when sensed outdoor temperatures are below a predetermined level, e.g. 40 F..degree..
By the same token the changeover thermostats prevent the auxiliary heating units from operating when outdoor air temperatures exceed the predetermined level. In the event the heat pump unit malfunctions (for example the compressor has failed in some manner), if the changeover thermostat prevents the auxiliary heating unit from being operated, the system is incapable of heating the indoor air when outside air temperatures are above the predetermined level but nevertheless cold enough that heating is required. (e.g. 45 F..degree.).
In order to enable the systems to operate on a temporary, emergency basis when heating is required but cannot be provided by the heat pump unit, proposals have been made for providing an emergency heat switch which functions to shunt the changeover thermostat switch and enable operation of the auxiliary heating unit. This proposed solution to the requirement for an "emergency heat" capability is costly and adds to the complexity of the systems.